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Limewater is the common name for a saturated aqueous solution of
Resultant carbon dioxide passed through limewater in the right tube, producing a milky solution due to
Limewater is the common name for a saturated aqueous solution of calcium hydroxide
Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed or slaked with water. It has ma ...
. Calcium hydroxide, Ca(OH)2, is sparsely soluble at room temperature in water (1.5 g/L at 25 °C). "Pure" (i.e. less than or fully saturated) limewater is clear and colorless, with a slight earthy smell and an astringent/bitter taste. It is basic in nature with a pH of 12.4.
Limewater may be prepared by mixing calcium hydroxide (Ca(OH)2) with water and removing excess undissolved solute (e.g. by filtration). When excess calcium hydroxide is added (or when environmental conditions are altered, e.g. when its temperature is raised sufficiently), a milky solution results due to the homogeneous suspension of excess calcium hydroxide. This liquid has been known traditionally as milk of lime.
Chemistry
An experiment commonly used to demonstrate the interaction of CO2 and Ca(OH)2 is as follows.
Resultant carbon dioxide passed through limewater in the right tube, producing a milky solution due to precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
of the insoluble suspension of calcium carbonate:
: Ca(OH)2 + CO2 → CaCO3 + H2O
If excess CO2 is added: the following reaction takes place:
: CaCO3 + H2O + CO2 → Ca(HCO3)2
The milkiness disappears since calcium bicarbonate is water-soluble.
Applications
The above chemical properties are commonly used for testing the presence of carbon dioxide in gaseous samples in school laboratories, and refining ofsugar
Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or do ...
in a process called carbonatation.
Industry
Waste gases from industries containing sulphur dioxide can be cleaned by bubbling through limewater, a process called sulfation, in which the toxic sulphur dioxide is trapped as a precipitate: : Ca(OH)2 + SO2 → CaSO3 + H2OWater treatment
Limewater is used in a process known aslime softening Lime softening (also known as lime buttering, lime-soda treatment, or Clark's process) is a type of water treatment used for water softening, which uses the addition of limewater (calcium hydroxide) to remove hardness (deposits of calcium and magnes ...
to reduce water hardness. It is also used as a neutralizing agent in municipal waste water treatment.
Arts
In buonfresco
Fresco (plural ''frescos'' or ''frescoes'') is a technique of mural painting executed upon freshly laid ("wet") lime plaster. Water is used as the vehicle for the dry-powder pigment to merge with the plaster, and with the setting of the plast ...
painting, limewater is used as the colour solvent to apply on fresh plaster. Historically, it is known as the paint whitewash
Whitewash, or calcimine, kalsomine, calsomine, or lime paint is a type of paint made from slaked lime (calcium hydroxide, Ca(OH)2) or chalk calcium carbonate, (CaCO3), sometimes known as "whiting". Various other additives are sometimes used.
...
.
Personal care and adornment
Treating one's hair with limewater causes it to stiffen and bleach, with the added benefit of killing any lice or mites living there.Diodorus Siculus
Diodorus Siculus, or Diodorus of Sicily ( grc-gre, Διόδωρος ; 1st century BC), was an ancient Greek historian. He is known for writing the monumental universal history '' Bibliotheca historica'', in forty books, fifteen of which ...
described the Celts
The Celts (, see pronunciation for different usages) or Celtic peoples () are. "CELTS location: Greater Europe time period: Second millennium B.C.E. to present ancestry: Celtic a collection of Indo-European peoples. "The Celts, an ancient ...
as follows:
"Their aspect is terrifying... They are very tall in stature, with rippling muscles under clear white skin. Their hair is blond, but not only naturally so: they bleach it, to this day, artificially, washing it in lime and combing it back from their foreheads. They look like wood-demons, their hair thick and shaggy like a horse's mane. Some of them are clean-shaven, but others – especially those of high rank, shave their cheeks but leave a moustache that covers the whole mouth...".
Food preparation
Limewater is used in the preparation of maize for corn tortillas and other culinary purposes using a process known as nixtamalization. Nixtamalization makes theniacin
Niacin, also known as nicotinic acid, is an organic compound and a form of vitamin B3, an essential human nutrient. It can be manufactured by plants and animals from the amino acid tryptophan. Niacin is obtained in the diet from a variet ...
nutritionally available and prevents pellagra. Traditionally lime water was used in Taiwan
Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the no ...
and China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
to preserve persimmon and to remove astringency
An astringent (sometimes called adstringent) is a chemical that shrinks or constricts body tissues. The word derives from the Latin ''adstringere'', which means "to bind fast". Calamine lotion, witch hazel, and yerba mansa, a Californian plan ...
.
Other uses
Limewater is widely used by marine aquarists as a primary supplement ofcalcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
and alkalinity for reef aquariums. Coral
Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and se ...
s of order Scleractinia
Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyps and have a cylindrical body crowned by an oral disc in which a ...
build their endoskeletons from aragonite (a polymorph of calcium carbonate). When used for this purpose, limewater is usually referred to as ''Kalkwasser''. It is also used in tanning and making parchment
Parchment is a writing material made from specially prepared untanned skins of animals—primarily sheep, calves, and goats. It has been used as a writing medium for over two millennia. Vellum is a finer quality parchment made from the skins ...
. The lime is used as a dehairing agent based on its alkaline properties.''The Nature and Making of Parchment'' by Ronald Reed
Calcium hydroxide is also applied in a leather process called liming.
References